In the oil and gas industry, geophysical prospecting is commonly used to aid in the search for and evaluation of subterranean formations. Geophysical prospecting techniques yield knowledge of the subsurface structure of the earth, which is useful for finding and extracting valuable mineral resources, particularly hydrocarbon deposits such as oil and natural gas. One technique of geophysical prospecting is a seismic survey. In a marine seismic survey, the seismic signal will first travel downwardly through a body of water overlying the subsurface of the earth.
Seismic energy sources (active seismic sources) are generally used to generate the seismic signal. Conventional energy sources for marine seismic surveys include air guns, water guns, marine vibrators, and other devices for generating acoustic wave-forms. After the seismic signal propagates into the earth, it is at least partially reflected by subsurface seismic reflectors. Such seismic reflectors are typically interfaces between subterranean formations having different elastic properties, specifically wave velocity and rock density, which lead to differences in acoustic impedance at the interfaces.
The reflections may be detected by marine seismic sensors (also called receivers) in an overlying body of water or alternatively on the sea floor. Conventional types of marine seismic sensors include particle-velocity sensors (geophones), water-pressure sensors (hydrophones), and other types of sensors. The resulting seismic data may be recorded and processed to yield information relating to the geologic structure and properties of the subterranean formations and their potential hydrocarbon content.
Note that the figures provided herewith are not necessarily to scale. They are provided for purposes of illustration to ease in the understanding of the presently-disclosed invention.